1. Field of the Invention
The present invention relates to an optical structure observation apparatus and a structure information processing method of the same, and particularly relates to an optical structure observation apparatus characterized by display processing of structure information in a middle layer of a measured object having a layer structure and a structure information processing method of the same.
2. Description of the Related Art
In recent years, as one of the methods for non-invasively obtaining the tomographic images of the insides of living bodies in, for example, a medical field or the like, optical coherence tomography (OCT) measurement has come to be used. As compared with ultrasound measurement, the OCT measurement has the advantage that the resolution is about 10 μm and one digit higher, and the detailed tomographic images of the insides of living bodies can be obtained. Further, a plurality of images are acquired while the position is shifted in the direction vertical to a tomographic image, and a three-dimensional tomographic image can be obtained.
For example, a large intestine forms a layer structure of a mucosal layer, a muscular layer of mucosa, a submucosa, muscularis propria and the like as shown in FIG. 17, and as shown in FIG. 18, ducts (crypts) are formed to be regularly arranged substantially vertically in the mucosal layer with the muscular layer of mucosa as a basal plate (“Large Intestine Pit Pattern Diagnosis” written and edited by Shinei Kudo).
For example, in the endoscopic diagnosis of large intestine cancer, ducts (crypts) are observed under endoscope, and classification according to the mucosal structure of a large intestine called a pit pattern is performed. However, pit pattern diagnosis is only the method for determining the progress based on the image of a mucosal surface, and information relating to the depth of invasion is only empirical.
When a large intestine mucosa is measured three-dimensionally by the aforementioned OCT measurement, the three-dimensional structure of a duct structure can be extracted, and as the information of the region near the surface, the structure similar to the pit pattern can be obtained. Further, since the three-dimensional structure can be obtained in the OCT measurement, change in the depth direction of the duct structure is observed.
It is known that the duct structure of a mucosal layer crumbles when cancer is caused in a large intestine (“Large Intestine Pit Pattern Diagnosis” written and edited by Shinei Kudo). More specifically, normal crypt forms the shape (normal state) as type I of FIG. 18, but it is known that due to canceration, the shape of a crypt deforms as in FIG. 19, for example, and the crypt itself finally crumbles as shown in FIG. 20 (lesion state).
Meanwhile, it is known that by three-dimensionally reconstructing a tomographic image by OCT measurement, extracting the crypt from the tomographic image, and analyzing the shape, difference between a normal part and a lesion part can be numerically analyzed (Journal of Biomedical Optics Vol. 13, p. 054055 (2008)). However, with extraction of the crypt, the structure is not visually understandable, and it is difficult to image a change in the stereoscopic lesion part.
Further, an art is disclosed, in which the surface of a measured object of a three-dimensional structure is extracted and made planar, and the structure information is imaged as a change in the depth direction (Japanese Patent Application Laid-Open No. 2007-225349).
However, for example, in the case of a large intestine, to what degree the lesion part approaches the muscular layer of mucosa, and whether invasion to the muscular layer of mucosa is present or not are important for cancer diagnosis. However, if a mucosal surface is made planar by using the art of Japanese Patent Application Laid-Open No. 2007-225349, ducts (crypts) are formed substantially vertical in the mucosal layer with the muscular layer of mucosa as a basal plate in the optical structure information as shown in FIG. 21, and therefore, the orientations (arrows 900 in FIG. 21) of the ducts (crypts) become random orientations, and there is the problem that visual judgment of the state of the ducts (crypts)(normal state of FIG. 18, or the lesion states of FIGS. 19 and 20) becomes difficult.